Objectives:
Students will be able to:
-Identify crystals
-Understand how crystals are formed
-Understand that crystals have six basic shapes
-Compare crystals of various substances
-Observe that crystals can be recovered by various means
Apparatus Needed:
Something porous: piece of brick
lump of charcoal
piece of cement
Table salt Saucepan
Water Hot plate
Laundry bluing Several tall instant
Household ammonia coffee jars
Sugar Pencil
Alum (available at drugstores) Paper clip
Salol (Phenyl salicylate) Several petri dishes
Food coloring Overhead projector
Cotton thread Hand lenses
Several shallow Poster paper
glass bowls Large and small
Craft wire styrofoam balls
Recommended Strategy:
1. Before the lesson is presented, grow one or more crystal gardens,
and recover a variety of crystals from solutions. You may use salt,
sugar, alum, or other compounds of your choice. (See Borgford and
Summerlin, Chemical Activities, American Chemical Society)

2. To introduce the lesson, display the crystals you have grown, along with saucers or petri dishes of salt, sugar, and alum granules. Do not identify the items by name, merely by number. Allow the children about ten minutes to observe the items on display in detail with a hand lens, comparing and contrasting them as they study them. A discussion of their observations should follow.

3. Review the three states of matter-solids, liquids, and gases- and their properties. Present the concept of amorphous and crystalline solids. A transparency showing the structure of each should be projected on the screen during the discussion.

4. Narrow the discussion to salt crystals. Show a transparency and a model of a unit cell of salt and a salt lattice. (The model can be made with the craft wire and the styrofoam balls.) Discuss how the lattices form. Refer to the items on display, reminding them that what they are seeing are lattices, not individual units.

5. Discuss the six basic shapes of crystals, while displaying an example of each shape on a transparency. Relate these examples to the crystals the children have already observed from the examples.

6. Review the definition of a saturated solution, and discuss how each of the sample items was made. Discuss the fact that crystals are formed through cooling and evaporation. Explore the concept that crystals can be recovered from vapors, molten materials, and solutions. Give examples of each in nature. (Snowflakes, diamonds, and salt crystals would be an example of each.) The slower the evaporation or cooling process, the larger the crystal.

7. To visually demonstrate crystal formation, heat a small amount of phenyl salicylate in a petri dish on a low setting on the hot plate until the crystals melt. Put the petri dish on the overhead. Seed it with a pinch of phenyl salicylate and watch as the liquid cools, and the crystals begin to form. The process can be repeated many times with the same petri dish. Simply warm it again until the crystals disappear, and repeat the process.

8. Orally review the concepts taught.

Additional Activities
Children can grow their own crystals and record their observations.
Children can compare the growth rates of various crystals, and
graph their results.
Children can investigate the effects of light on various crystals.
Children can investigate the properties of a variety of crystals.
Additional References
Brown and Forsyth, The Crystal Structure of Solids, Crane and Russak,N.Y. 1973.